CNC Spindle Maintenance and Repair

      Careless servicing can cost in terms of equipment life. Here's a useful example and a discussion of smart maintenance practices. April 17, 2009

The spindle taper on our router became galled, I think due to the operator not keeping it clean. He claimed to have cleaned it every morning, but when asked how it looked, he said he had never looked up into the taper or even felt it to verify it was clean. Just went through the motions. The cut quality had been deteriorating and finally the tool holder came loose. When I checked the problem, the tool holder had spun in the socket, which was glazed with wood powder and had galled the metal. I found a company in MO that said they could grind the spindle taper in place on the machine for $2145. Hired. They had lots of experience and successfully ground the spindle. The machine now runs perfectly smooth, nice cut. There was a clue that there were problems developing, but no one said anything. Not the first time that something has shown signs, but the employee just kept running it until it failed. The procedure for grinding the taper turns out to be fairly simple.

Forum Responses
(CNC Forum)
From contributor T:
Any feedback on the Nemi Spindle Socket cleaning tool? Looks like a great PM tool.

From contributor J:
Please re-post and let us know when the first tool holder comes flying out of the spindle!

From the original questioner:
What makes you think it won't work? It's a common practice in the machine tool industry. The fit was checked with a new tool holder and dye. The stud tension was unchanged. To lose a tool, the pull stud or fingers will have to fail.

From contributor B:
When they ground the taper, did they check the pull stud grips? If the tool holder spun, then it could have had a negative effect up there as well. Other than that I see no reason for anything to fail. I'm certainly no expert on this, but it would seem the removal of a few thousandths of material will allow for the tool holder to seat slightly higher up into the cone. As long as there is enough room before the grab ring above the nut bottoms out, it would be fine.

I can sympathize with the employee inattention issue. I instituted was we call "machine Monday" to deal with that. Every Monday morning we service a different group of machines in the shop. All machines break down into the first, second, third or fourth Monday of the month. That way every machine gets a thorough going over once a month.
Since starting this, the guys are much more in tune with the equipment. Things that don't feel or sound right get brought to my attention much sooner than they used to.

From contributor R:
There is no reason this shouldn't work. The pull stud has a certain amount of upward motion available to it. With a brand new cone and spindle, the pull stud would be near the bottom of its throw. As the cone and spindle wear (albeit a tiny amount) the draw bar is able to seat the cone just as securely as before. The draw bar is air powered, so the pull force is always the same, provided the air pressure remains the same.

As far as maintenance is concerned, it's hard to stress the importance of it too much. As a former armorer with the Army, maintenance was always key, and my experience with shop machines has only reinforced that.

The "Maintenance Monday" plan is fantastic. I work diligently with my clients to work up a firm maintenance schedule. The hardest part is taking the time to do it no matter how tight the work schedule. Inevitably, if you don't, the machinery will fail, and the downtime for repair will virtually always cost you a lot more than the maintenance time.

From the original questioenr:
Actually, I think the tool holder is released by air, but held up by star washer type springs. The same type of system used on some molder spindles. If you look up into the taper you can see the fingers are closed when there is no air. The reason for doing it by spring load is it's on the safe side. Loss of air won't release the tool holder. The disadvantage is the limited take up of that type of spring system, but they are adjustable.

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